Radio frequency identification (RFID) is a technology that recognizes, traces, and manages objects or animals with a tag attached by obtaining or recording information from the tag having unique identification information in contactless manner using a radio frequency (RF).
In general, the RFID includes a RFID tag including unique identification information and attached at an object and an animal and a RFID reader for receiving information from the tag or writing information to the tag. The RFID is classified into a mutual induction type and an electromagnetic type according to a communication method between the reader and a tag, or into a long wave type, a medium wave type, a short wave type, and a microwave type.
A RF unit having a reader, often referred as an interrogator, is a portable unit or a stationary unit for receiving a signal from the RFID tag and decodes the received signal.
When a plurality of RFID tags are in the tag-recognizable coverage of the RFID reader, a plurality of a RFID tags in the tag-recognizable coverage simultaneously respond to the signal of the RFID reader, thereby arising a collision problem.
Therefore, an anti-collision algorithm is required to identify a plurality of tags. The anti-collision algorithm is generally divided into a tree-based deterministic algorithm and a slot-aloha based probabilistic algorithm.
Recently, a UHF band has been recognized as a band suitable for the distribution industry. In order to satisfy the strong demand of the RFID market, the related standard has been rapidly progressed compared to other frequency bands. Among the introduced standards, ISO/IEC 18000-6 A, ISO/IEC 18000-6 C, 18000-7, and EPC C1 use the slot aloha based anti-collision algorithm.
In the slot aloha based anti-collision algorithm, a transmission time is divided into a plurality of time slots, and each tag selects one of time slots and transmits data using the selected time slot. In a general RFID system, a reader transmits a command with the number of slots as a parameter to each of tags in the coverage thereof. Then, each of the tags generates a random number, selects a slot, loads the information to transmit into the corresponding slot, and responds to the reader. Although a slot having one information is recognized by a reader, a slot having a plurality of information, a slot with collision generated, is not recognized by a reader. Herein, the slot having one information denotes a slot occupied by one tag or is referred as an identification slot. The slot having a plurality of information is a slot occupied by a plurality of tags. Due to the collision, the tags must retransmit the information in the next round or the next frame.
In order to effectively identify tags, the number of slots is set to have higher system efficiency, that is, a higher rate of identification slots in entire slots. Excessively large number of slots compared to the number of tags causes slots to be wasted, and excessively small number of slots compared to the number of tags increases a collision generation rate among tags. That is, the number of tags in the same coverage and the set number of slots decide the system efficiency.
Conventionally, a RFID tag and a RFID reader are independent devices. There is no tag/reader integrated RFID apparatus and a method thereof introduced lately.
Therefore, there is a demand for developing a tag/reader integrated RFID apparatus that performs both of a tag function and a reader function and a method of controlling a tag and a reader in the tag/reader integrated RFID apparatus without collision.